1. Field of the Invention
The invention relates to optical disc drive and in particular to automatic power control system for optical disc drive and a method thereof.
2. Description of the Related Art
In an optical disc system, a disc drive accesses an optical disc by a laser beam driven by a laser diode therein. To accurately record and play data to and from the optical disc, the disc drive utilizes an automatic control system for power and servo control to drive the laser diode.
FIG. 44 is a block diagram of a conventional automatic power control system, comprising analog preprocessing unit 6110, comparator 6112, and analog post processing unit 6114. Analog preprocessing unit 6110 is coupled to comparator 6112, and subsequently to analog post processing unit 6114.
During an automatic power control process, analog preprocessing unit 6110 is opened for invalid input data Sin, and closed for valid data. Analog preprocessing unit 6110 receives analog feedback signal Sin and processes it to generate preprocessed signal Spre. Comparator 6112 obtains preprocessed signal Spre for comparison with a target value Dtarget, and, based on differences therebetween, generates error signal Se. Analog post processing unit 6114 generates a control signal Sc in response to error signal Se. Analog feedback signal Sin indicates power level of the laser beam that reads data from an optical disc. When analog feedback signal Sin is invalid, analog preprocessing unit 6110 is opened to stop data processes. Target value Dtarget is a predetermined power level. When preprocessed signal Spre does not equal target value Dtarget, analog post processing unit 6114 determines control signal Sc according to error signal Se to increase or decrease the driving current of the laser diode, thereby controlling the power level of the laser beam to a level where preprocessed signal Spre equals target value Dtarget.
FIG. 45 is a block diagram of a conventional automatic power control system, comprising analog-to-digital converter (ADC) 6220, digital preprocessing unit 6222, comparator 6224, digital post processing unit 6226, and digital-to-analog converter (DAC) 6228. Analog to digital converter (ADC) 6220 is coupled to digital preprocessing unit 6222, comparator 6224, digital post processing unit 6226, and subsequently to digital-to-analog converter 6228.
Automatic power control system 622 provides digital automatic power control to the power level of input signal Sin. Analog-to-digital converter 6220 samples analog feedback signal Sin in a predetermined data rate to generate sampled data Ds. Digital preprocessing unit 6222 performs processes such as filtering on sampled data Ds to generate preprocessed data Dpre, compared with target value Dtarget in comparator 6224 to provide error data De. Digital post processing unit 6226 converts error data De to post processed signal converted to analog control signal Dc in Digital-to-Analog converter 6228 for controlling the driving current of the laser diode such that the power level of the laser beam is kept at a desirable level.
As technology moves from analog to digital, a need exists for an efficient and accurate digital automatic control circuit.